This application for a K23 Mentored Career Development Award incorporates a focused course of study, detailed research plan, and structured mentoring environment intended to train Emily Oken, MD, for a career in patient-oriented research. Dr. Oken, who is currently a General Internal Medicine research fellow, will draw upon her previous experience performing epidemiologic research focused upon nutrition and health risk behaviors, as well as clinical expertise in internal medicine, women's health, and pediatrics. A woman's nutrition during pregnancy helps determine the outcome of her pregnancy and the lifelong health of herself and her child. The proposed study will examine the effects of the ratio of n-3 to n-6 fatty acids consumed by a woman during pregnancy upon fetal growth, length of gestation, and child cognition through age 3 years. Additionally, characteristics of women who consume a low dietary ratio of n-3 to n-6 fatty acids will be identified, to help those making dietary choices and recommendations. Data for this proposal are being collected through Project Viva, an ongoing NIH-funded longitudinal prospective cohort study of approximately 2700 pregnant women and their children. The prospective design, large sample size, and breadth of available covariate information in Project Viva provide an ideal foundation for the proposed analyses. Dr. Matthew Gillman, the Principal Investigator for Project Viva, will serve as the primary mentor for Dr. Oken's research. Additionally, an Advisory Committee comprised of experts in nutritional epidemiology, the effects of prenatal fatty acids, epidemiologic methods, and biostatistics will assist Dr. Oken with issues of study design and analysis, as well as career development. Dr. Oken wilt also take courses at the Harvard School of Public Health to develop advanced knowledge of nutritional epidemiology, in particular the health effects of polyunsaturated fatty acids, and epidemiologic methods necessary for the implementation of this project, such as the case-cohort study design and analysis of longitudinal data.